Improvement in screw-propellers



'1. C. CROSS.

Screw-Propellers.

N0 H52 Q73 I Pat ented1uly14,1874.

UNITED STATES PATENT @EEIOEo JOHN o. onoss, OE BROOKLYN, NEW YORK.

IMPROVEMENT IN SCREW-PROPELLERS.

Specification forming part of Letters Patent No. 152,973, dated July 14, 1874 application tiled May 2, 1874.

To all whom it may concern:

Be it known that I, JOHN C. CROSS, of Brooklyn, in the county of Kings and State ot' New York, have invented an Improvement in Propellers for Vessels; and the following is declared to be a correct description of the same.

Screw-propellers usually are made with the Vshanks ofthe blades in the same plane ot' revolution as the outer ends ot' the blades hence the portion Ot' the water that is contiguous to the shank or base of the blade is continuously operated upon, and its centrifugal velocity increased, until it is thrown ofi' from the end of the blade; thereby the resistance of the water to the blade is lessened and the water greatly agitated.

The object ot' my invention is to lessen the centrifugal action ot' the blade iu the water, to cause the different portions ot' the blade to come into contact with water that is allowed to remain as quiescent as possible, and thereby form a more iirni resistance to the incline or screw ofthe propeller.

I Ina-lie each propeller-blade a in the general form of a compound incline or twisted plate usually employed; but the front edge b is in a plane standing radially to the shaft, as seen in the elevation, Figure 1, and inclined backwardly as a parabolic curve, represented in the side view, Fig. 2.

The base or shank of each blade where it joins the hub c is not as wide as the outer edge or end t' ot' the blade, and hence the back edge o of the blade will extend backwardly in a parabolic curved line, as seen in Fig. 2; but said back edge lies in a plane that is radial to the shaft of the propeller.

ln consequence ofthe shape of the propellerblades, as aforesaid, they act more eliiciently in propelling a vessel, because the centrifugal force is lessened Without lessening the surface ofthe blade that acts upon the water; hence the Water will remain more solid, and the propeller will move through the water with less agitation to the latter.

rlhe compound curved plancot the propeller blade may be such that when viewed at the end of the blade, as in Fig. 3, it may be a straight line, or nearly so; but I nd it advantageous to curve the blade additionally, as illustrated in Fig. 4, the curve at r bringing the rear part ot' the propeller-blade to a less inclination to a radial plane, and hence the water will leave the blade more in a rearward direction, and not be thrown oft' centrifugally to as much extent as usual.

The side ot' the blade that is usually operative is made nearly straight, especially at the base near the hub, and the other side ot the base ot' the blade is convexedA to obtain the required strength. This propeller can be used in backing as well as the ordinary propeller, but the lines of the blades are made with special reference to the forward movement ofthe vessel.

I claim as my inventionrIhe screw-propeller made with blades that incline backwardly, and the front and back edges of each blade are in planes that are radial to the propeller-shalt, but such edges are curved rearward, as and for the purposes set forth. V

Signed by lne this 29th day ot April7 A. D. 1874.

JOHNV C. CROSS.

Witnesses:

GEO. T. PINOKNEY, y CHAs. H. SMrrr-I. 

